Hi,
I'd suggest that you contact customer support and send it in to Kemper (if you haven't already).
They attempted to fix mine and couldn't find the problem. It occurs randomly and I was never able to record it or make it happen deliberately. So they just made sure everything was working and sent it back to me.
So, just recently, I sent them the link to your audio clip (which is very similar to my problem) and they're sending me a new Powerhead!
Thank-you for sharing that clip! It saved me, big time!!!
And I sincerely hope that either you or Kemper resolve your problem!